Years ago, I had a great check register application on my Palm and I loved it. It simply monitored money in and out with some basic categorization. That's what we're after, and Cha-Ching sounds like it's going in the right direction.
You can monitor your budget and enter location-aware transactions. There's good news for owners of the desktop version, too. Namely, transaction histories will sync to the iPhone client via WiFi. Neat.
There's a demo video here. It's a nice looking app, that's for sure. You can currently pick it up from The App Store for an introductory price of $2.99US. Again, we'll let you know what we think after we've put it through its paces.